Personal space
Thai anatomy has its own special considerations. Thais believe that the head - the most sacred part of the body - is inhabited by the kwan, the spiritual force of life. Never pat a Thai on the head even in the friendliest of circumstances. Standing over someone older, wiser, or more enlightened than yourself - is also considered rude behavior since it implies social superiority. As a sign of courtesy, lower your head as you pass a group of people. When in doubt, watch the Thais.
Conversely, the foot is considered the lowest and dirtiest part of the body. The worst possible insult to a Thai is to point your unholy foot at his sacred head. Keep your feet under control; fold them underneath when sitting down, don't point them toward another person, and never place your feet on a coffee table.
The left hand is also unclean and should not be used to eat, receive gifts, or shake hands. Aggressive stances such as crossed arms or waving your arms are also consider boorish.